A woman boards a train at an underground station on March 5, 2012, in London. The rail system, which carries a quarter of a million people around its network every day, is celebrating its 150th anniversary. Dan Kitwood, Getty Images

Six underground railway tunnels run under the Earl's Court Exhibition building, which was under construction, on May 6, 1930, near Earl's Court Station. Harry Shepherd, Getty Images

People shelter from German air raids on Dec. 5, 1940, at Bound's Green Station. M. McNeill, Getty Images

Piccadilly Line undergound trains are parked outside Northfields Depot on March 29, 2001, in west London. Adrian Dennis, AFP/Getty Images

A Picccadilly Line train heading to Heathrow waits at Northfields Station on Aug. 28, 2003, after a major power failure in London put rail networks out of action during rush hour. Jim Watson, AFP/Getty Images

Davinia Turrell, left, holds a bandage over her face as Paul Dadge helps her to safety at Edgware Road Station on July 7, 2005, after a series of explosions ripped through London's Underground rail and bus network. Gareth Cattermole, Getty Images

People walk along the platform on July 22, 2005, at Earl's Court Station during the evening rush hour. Nicolas Asfouri, AFP/Getty Images

Maintenance workers clean up an area on Nov. 18, 2008, after welding track joints in a tunnel on the Victoria line. Peter Macdiarmid, Getty Images

A train enters a station on Feb. 14, 2012. Dan Kitwood, Getty Images

People enter Stratford Station on July 14, 2012. Kirby Lee, USA TODAY SPORTS

A person rushes through Stratford Station on July 16, 2012. Joe Toth, USA TODAY SPORTS

Passengers walk between platforms seven and six on July 24, 2012, inside of the Euston tube. Andrew Weber, USA TODAY SPORTS

Passengers pack onto a Central Line train at Tottenham Court Road Station on July 31, 2012. Andrew Cowie, AFP/Getty Images

A restored steam engine built in 1898, known as Met Locomotive No. 1, travels through the Baker Street Underground station on Dec. 16, 2012. The train was on a practice run for a commemorative trip to celebrate the 150th anniversary of the London Underground. Oli Scarff, Getty Images

A commemorative sign hangs at the Baker Street station on Jan. 8, displaying the date when the station was opened. Alastair Grant, AP